Population Growth and Resource Availability (3.5)

Size (N)

• total # of individuals  in a given area at a given time
• larger size (N)
• safer from population decline

Density

• number of individuals/area
  • Higher density
  • higher competition, possibility for disease outbreak, possibility of depleting food source

Distribution

• how individuals in a population are spaced out compared to each other
  • random: trees
  • uniform: territorial animals
  • clumped: herd/group animals

Sex Ratio

• ratio of males to females
  • closer to 50:50 ideal for breeding
  • die off or bottleneck effect can lead to to skewed sex ratio (not enough females) limiting pop. growth

Density-Dependent-Factors

• factors that influence population growth based on size
• Examples
  • food
  • light
  • competition for habitat
  • water
  • disease
• All these things limit population growth based on their size

Density-Independent Factors

• factors that influence population growth independence of their size.
• examples
  • natural disasters
  • floods
  • hurricane tornado
  • fire
• It doesn’t matter how big or small a pop. is, natural disasters limit them both

Ex. of Density-Dependent Factor

• Food is a density dependent factor. (also a limiting resource)

• When twice as much food was added to the dish, both species increased carrying capacity by about 2x

• Biotic Potential

• Max potential growth rate with no limiting resources

• May occur initially, but limiting resources (competition, food, disease, predators) slow growth, & eventually limit pop. to carrying capacity (k)

Biotic potential

• exponential growth

Logistic growth

• initial rapid growth, then limiting factors limit pop. to K

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